a) If your tooth isn't symptom free, it should be evaluated.

For the most part, if you have a tooth that's had root canal treatment and it continues to have, or has started to show, pretty much any type of symptom, it should be examined by your dentist.

The normal expectation is that, after an initial period of healing, successful treatment will result in an environment that allows your body to maintain those tissues that surround your tooth in a state of health. In the vast majority of cases, if this has been achieved the tooth will be totally asymptomatic.

b) How soon should you have your tooth evaluated?

As a general rule, the timing of your tooth's examination should be sooner rather than later.

That's because teeth that have endodontic problems are unpredictable (due the fact that they frequently harbor infections). So, don't procrastinate, the best plan is always to contact your dentist's office so they can make a determination about the urgency of your needs.

c) Not all problem teeth display symptoms you can detect.

Not all cases of failed endodontic treatment display obvious symptoms. A common scenario is one where from the patient's point of view a tooth seems perfectly fine but a dentist's x-ray examination (possibly as a part of a routine checkup) reveals a problem.

B) Why does root canal treatment fail?

Treatment failure indicates that either:

The cleaning aspect of the tooth's procedure was incomplete or ineffectual.

The seal that was created during treatment has not been successful in keeping contaminates from seeping in or out of the tooth. Either it was deficient initially, or else has since deteriorated.

Specific reasons why root canal treatment may fail.

Here are some examples of how the above problems may come about.

1) Branched canals

Root canals sometimes fork, and these divisions, which may be very minute, can be hard to detect and access. Because of this, one canal branch may be properly treated while the other is totally overlooked.

2) Overlooked canals

A tooth may have more individual root canals than the dentist has anticipated. And in these cases, and especially when the unexpected canals are very tiny, they may not be discovered. If not, they will remain untreated and a cause of problems.

Some cracked teeth may not be treatable.

3) Cracked teeth

Cracks that have formed within a tooth provide a space that can be colonized by bacteria. Unfortunately, unlike root canals that a dentist can access and then clean and seal, cracks can't be treated. That means, once an infection has established itself it can't be resolved and will be a persistent source of problems.

When performing treatment, a dentist may be unaware that a crack is present (in many cases they can be impossible to identify), or underestimate the significance of the ones they see. In other cases, the crack that has caused the tooth's problem formed after it received its original treatment (see below).

4) Deterioration of the seal

The seal that was created by a tooth's root canal treatment can deteriorate over time. If so, bacteria may reenter the tooth and reestablish an infection. Leakage of contaminates from within the tooth can be a source of constant irritation of the tissues that surround its root.

5) An inadequate dental restoration

A defective or inadequate final restoration (the "permanent" one placed after the completion of treatment) can allow contaminates to reenter a tooth. (The x-ray graphic above shows an example of this.)

This phenomenon is termed "coronal leakage" and it is a major cause of root canal failure. For more detailed information, use this link: What is Coronal Leakage?

6) Lack of clinician expertise.

Research has shown that treatment provided by endodontists (root canal specialists) has a higher success rate than that provided by general dentists.

For any clinician, providing treatment for some teeth will prove to be amazingly straightforward and then, with others, surprisingly involved. Unfortunately, fully comprehending the level of complexity of the task at hand may not be possible until treatment is underway.

C) Contributing / Complicating factors.

It's possible that your tooth's root canal treatment has been successful but the tooth itself has problems due to other factors.

a) The tooth has broken or fractured.

Teeth that have undergone root canal treatment are seldom as structurally sound as they were originally. And for this reason, they often require the placement of a dental crown for strengthening and protection.

If an endodontically treated tooth does break, it's not always a big problem.

Assuming that the damage is confined to just the crown portion of the tooth (not the root), it's quite likely that the tooth can be rebuilt. (In some instances, the repair may require the placement of a dental post and core.)

If the crack extends into the tooth's root, a serviceable repair may or may not be possible (see above).

b) The tooth has extensive decay or gum disease.

Teeth that have had root canal treatment are at risk for the formation of tooth decay and gum disease, just like any other tooth. And if allowed to advance, either of these conditions can ultimately lead to tooth loss.

D) What's the fix for failed root canal treatment?

a) Retreatment

Root canal cases that have failed can be retreated. In most cases this involves repeating essentially the same procedure that was performed originally, with the exception that time must be committed to removing the previously placed sealing materials. We now discuss this topic here: Root canal retreatment.

Your dentist may offer to perform this work, or they may feel that the expertise of an endodontist is required.

b) Tooth extraction and replacement.

Besides retreatment, the only other option for a tooth with failed root canal is extraction and replacement. This option might be chosen because retreatment is impossible, it only offers a low success probability or its cost-effectiveness is questionable.

c) Timing your treatment.

Whatever type of follow-up treatment is chosen should be performed within the time guidelines recommended by your dentist. After performing an examination, they can gauge how much urgency appears to be involved.

Teeth with failed treatment can be unpredictable due to the fact that they frequently harbor infection, which has the potential to flare up (create pain and/or swelling) without warning. As a precaution, you dentist might write you a prescription for antibiotics, so you have them on hand if conditions with your tooth turn to the worse before treatment can be performed.